Among other factors, vision depends upon the transparency of an individual's lens. The lens, encapsulated by a cellophane-like membrane covering its anterior and posterior surfaces, focuses light entering the eye onto the retina. Opacity or cloudiness of the lens may prevent a clear image from forming on the retina. This condition, commonly known as a cataract, may be congenital or result from trauma, disease or age. When visual loss reaches a certain point, the lens may be removed and replaced by an intraocular lens.
Various techniques and procedures have been developed to remove a cataract. In perhaps the most popular technique, known as an extracapsular extraction procedure ("ECCE"), the anterior capsule is opened and the lens extracted and replaced. Opening the anterior capsule via an anterior capsulectomy is a very delicate procedure and is widely considered to be the most difficult step in an ECCE. Complications, including zonular stress, vitreous loss, large capsular tags, and difficulties in nucleus expression are unfortunately frequent, causing increased operative duration and frequency as well as pain and discomfort for the patient. A more thorough review of various procedures and their associated complications is found in Phacoemulsification and Aspiration of Cataracts, Chapter 10 (1979)(Emery, J. M. and Little, J. H. eds.), incorporated herein by reference.
A variety of devices have been developed to cut or tear the anterior capsule to facilitate removal of the lens. Perhaps the most common device is a cystotome. When cataracts are removed by an ECCE, a cystotome is inserted through a small incision in the sclera or peripheral cornea and small connecting tears are made in the anterior lens capsule in a circular pattern around the periphery of the lens capsule. The tears are subsequently connected to form a complete circle. The resulting circular piece of the anterior capsule is then removed and the lens extracted.
The phacoemulsification method of cataract removal requires a different type of anterior capsular opening. During phacoemulsification, there is a great deal of tension on the cut edges of the anterior capsule while the lens nucleus is emulsified with ultrasound energy. Accordingly, for this method, a tagless, continuous cut or tear is a critical step for safe and effective phacoemulsification. If the capsule is opened with numerous small capsular tears, as in the above-described extracapsular technique, the small tags which remain can lead to capsular tears which may extend posteriorly to the posterior capsule. Such a radial tear constitutes a complication since it destabilizes the lens for further cataract removal and safe intraocular lens placement within the lens capsule later in the operation. More importantly, once the posterior capsule is punctured, the vitreous humor behind it gains access to the front of the eye. If the vitreous enters the front of the eye through a hole in the posterior capsule, the vitreous must be removed by an additional procedure with special instruments. The loss of vitreous also is associated with an increased rate of subsequent retinal detachment and/or infection within the eye. Importantly, these complications are potentially blinding.
In addition to the above-identified complications with extracapsular extractions and phacoemulsification, several other disadvantages are associated with the devices and methods currently employed for the procedures. Prior art devices and methods used to produce a continuous curvilinear capsular opening require extraordinary skill and technique by the surgeon performing the operation. This is due to the extreme difficulty in controlling the path of the device.
For example, the most typical method begins with a capsular incision made with a cystotome. This incision is then coaxed to form a circular or oval shape by pushing the leading edge of the freshly tearing capsule with the cystotome in a non-cutting fashion. Alternatively, the initial capsular incision is torn into a circular shape by grasping the leading edge with fine caliber forceps and advancing the cut in a very uncontrolled manner. This is a very challenging maneuver and, even in the most experienced hands, the tearing motion can lead to an undesirable tear of the capsule toward the back of the lens. Moreover, even if a tagless edge is ultimately produced, the size and/or position of the capsular opening presents a problem. For example, a small capsular opening can impair the safe removal of the lens nucleus and cortex and prevent proper intraocular lens insertion into the lens capsule. The additional stresses necessary to accomplish the operation with a small or misplaced capsular opening put the eye at risk for zonular and capsular breakage. Both of these types of breakage will likely increase the length and complexity of the operation and can result in vitreous loss.
A continuous, properly positioned and circular opening is highly desirable since it results in: (1) a significant reduction in radial tears and tags within the anterior capsule, (2) capsule integrity necessary for proper centering of a lens prosthesis; (3) safe and effective hydrodissection; and (4) safe use of capsular procedures on patients having poorly visualized capsules and/or small pupil openings.
Prior devices employed in performing an anterior capsulectomy include manual and mechanical techniques for severing the anterior lens capsule of the eye. For example, U.S. Pat. No. 4,570,632 to Woods describes a cystotome which produces a continuous series of perforations. Additionally, U.S. Pat. No. 4,706,669 to Schlegel describes a device for perforating the lens capsule using a wire connected to a drive motor. A more recent device includes the use of a manually controlled rotating blade (U.S. Pat. No. 5,423,841 to Kornfeld).
In most prior known devices, it is difficult to cleanly cut the anterior capsule without leaving residual "tags" or tears in the capsule. Additionally, these devices either cause sufficient drag on the capsule and upset the nucleus of the lens, or place stress on the zonular structure. More importantly, most of these devices offer the surgeon little or no control over the exact placement of the cutting edge during the procedure and require exceptional skill and control to avert undesired results (e.g., tags, irregular cutting path, etc.). Finally, most of these devices do not provide a continuous, properly positioned, circular opening in the anterior capsule.
Most, if not all, of the problems associated with the above-described prior art devices and methods are produced because use of the instrument or device requires movement of the instrument (i.e., the instrument does not remain stationary during the procedure). Movement of the instrument (e.g., through positioning and re-positioning the instrument and during the actual cutting portion of the procedure) produces damage to surrounding tissue (e.g., the endothelium of the cornea). Such damage increases: (1) the length of the procedure, (2) pain to the patient; (3) the number of complications; and (4) the recovery time, and is virtually unavoidable by the surgeon using such devices since movement is required to accomplish the procedure. Accordingly, there remains a need for a remotely operable intraocular cutting instrument specifically adapted for capsulorehexis procedures and capable of producing a continuous, circular, smooth, stress-free, tag-free cut along the anterior capsule to facilitate removal of the lens during a capsulectomy and requiring virtually no movement of the instrument once position to accomplish the procedure.